Brake squeal noise occurs upon application of a vehicle brake when the structure of the brake drum resonates at its natural frequencies due to forces imparted by the brake pad frictionally engaging the inner surface of the brake drum. The sound pressure level produced by the vibrating drum can become quite objectionable to receivers in the immediate area thereby prompting manufacturers of brake drums and other driveline components to modify the brake drums using various means to reduce vibration levels of the drum. Methods commonly used include adding dampening to alter the resonant qualities of the brake drum thereby reducing the amplitude of vibration so as to reduce the sound level produced when brake squeal occurs.
Prior art methods of reducing the vibrational amplitude of a brake drum have included adding various additional structures such as retention bands and/or dampening layers to the outside of the drum with varying degrees of effectiveness. The problem with these prior art approaches generally has been the complexity and expense introduced with the added components where the cost to benefit ratio has not proved to be practical. Another significant problem introduced whenever a layer of material is added to the outside structure of the brake drum is that the rate of heat rejection is dramatically reduced, thereby reducing the service life of the drum due to higher operating temperatures. Examples of these prior art methods can be found by reference to U.S. Pat. Nos. 2,349,658 and 2,639,195, the disclosures of which are hereby incorporated by reference.